In recent years, considering reducing the load on the environment, a lead-free piezoelectric ceramic composition has attracted attention. In general, lead-free piezoelectric ceramic composition is known to have a lower piezoelectric d constant than a lead-based piezoelectric ceramic composition, such as PbTiO3—PbZrO3 (PZT).
Under such circumstances, a (K, Na)NbO3-based piezoelectric ceramic composition, which has a relatively large piezoelectric d constant (piezoelectric distortion constant) among non-lead piezoelectric ceramic compositions, has been studied actively.
For example, Patent Document 1 discloses a piezoelectric ceramic composition containing a main component having a general formula of (1−n)(K1−x−yNaxLiy)m(Nb1−zTaz)O3−nM1M2O3 (wherein M1 is a bivalent metallic element, and M2 is a quadravalent metallic element). Patent Document 2 discloses a piezoelectric ceramic composition containing a main component having a general formula of (1−n)(K1−x−yNaxLiy)m(Nb1−zTaz)O3−nM1M2M3O3(wherein M1 is a trivalent metallic element, M2 is a monovalent metallic element, and M3 is a tetravalent metallic element). In Patent Documents 1 and 2, x, y, z, m, and n are in the ranges of 0.1≦x, y≦0.3, x+y<0.75, 0≦z≦0.3, 0.98≦m≦1.0, and 0<n<0.1.
In Patent Documents 1 and 2, a predetermined mol of a complex oxide M1M2O3 or M1M2M3O3 (for example, BaTiO3, CaTiO3, or (Na0.5Bi0.5)TiO3) of a perovskite type is dissolved as an additional component in (K, Na, Li)(Nb, Ta)O3. The resulting piezoelectric ceramic composition has a relative dielectric constant ∈r (=∈T/∈0; ∈T is the absolute dielectric constant, and ∈0 is the dielectric constant of free space) of at least 1000, an electromechanical coupling factor kp of at least 25%, and a Curie point Tc of more than 200 degrees C.
Patent Document 3 discloses a piezoelectric ceramic composition containing 0.005 to 0.15 mol of at least one metallic element selected from the group consisting of Ag, Al, Au, B, Ba, Bi, Ca, Ce, Co, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Ho, In, Ir, La, Lu, Mg, Mn, Nd, Ni, Pd, Pr, Pt, Rb, Re, Ru, Sc, Si, Sm, Sn, Sr, Tb, Ti, Tm, V, Y, Yb, Zn and Zr per one mol of a main component having a general formula of {Lix(K1−yNay)1−x}(Nb1−z−wTazSbw)O3 (wherein 0≦x≦0.2, 0≦y≦1, 0≦z≦0.4, and 0<w≦0.2) and has a percentage of open pores of 0.4% by volume or less.
Patent Document 3 indicates that the addition of the at least one metallic element selected from Ag to Zr described above to reduce the percentage of open pores (the volume percentage of hollows in the surface of a piezoelectric ceramic composition) to 0.4% by volume or less can improve the mechanical strength. In addition, Patent Document 3 indicates that since the piezoelectric ceramic composition contains a component having the general formula of {Lix(K1−yNay)1−x}(Nb1−z−wTazSbw)O3 as a main component, the piezoelectric ceramic composition can utilize a high piezoelectric d constant and a high electromechanical coupling factor kp of the compound having the general formula to have these excellent characteristics.
Patent Document 4 discloses a piezoelectric ceramic composition having a general formula of {(K1−xNax)1−yAgy}NbO3−z[Mα+][O2−]α/2 (wherein 0≦x<1, 0≦y≦0.1, 0≦z≦0.05, and 0<y+z; M denotes at least one metallic element selected from the group consisting of Mn, Mg, In, Si, Ga, and Sb), and α is the average valence of a metallic element M).
According to Patent Document 4, the addition of predetermined amounts of Ag and at least one metallic element selected from the group consisting of Mn, Mg, In, Si, Ga, and Sb to (K, Na)NbO3 can decrease the dielectric loss tan δ, improve the reliability, and increase the piezoelectric d constant.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 11-228227
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 11-228228
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2004-244300
[Patent Document 4] Japanese Unexamined Patent Application Publication No. 2002-68835